Oxygen scavenger accelerator

ABSTRACT

An iron-based oxygen scavenging packet is set forth in which the rate of uptake of oxygen is increased by virtue of the presence of an oxygen uptake accelerator such as water which is introduced into the packet. Methods of increasing the rate of oxygen absorption by the iron-based oxygen scavenging packet are also set forth.

RELATED APPLICATIONS

The present application is a continuation-in-part of pending U.S.application Ser. No. 09/346,752, filed Jul. 2, 1999, now U.S. Pat. No.6,315,921 B1 which is a continuation of U.S. application Ser. No.08/856,448, filed May 14, 1997, and issued as U.S. Pat. No. 5,928,560 onJul. 27, 1999, which is a continuation-in-part of U.S. application Ser.No. 08/700,644, filed Aug. 8, 1996, and now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to a device and method formaximizing the rate of oxygen uptake of an oxygen absorber. Moreparticularly, the invention relates to an iron based oxygen scavengingpacket having an improved composition for accelerating the rate ofoxygen absorption wherein the packet is specifically designed to be usedin a packaging system designed to keep meat fresh.

BACKGROUND OF THE INVENTION

Perishable foods, such as meats, fruits, and vegetables are typicallyplaced into packaging systems after harvesting in order to preservethese foods for as long as possible. Maximizing the time in which thefood remains preserved, especially the time between initial packaging atthe plant and delivery at the retail grocery store, increases theprofitability of all entities in the chain of distribution by minimizingthe amount of spoilage.

The environment in which the food is preserved is a critical factor inthe preservation process. Not only is maintaining an adequatetemperature important, but the molecular and chemical content of thegases surrounding the food is important as well. By providing anappropriate gas content to the environment surrounding the food, thefood can be better preserved when maintained at the proper temperatureor even when it is exposed to variations in temperature. This gives thefood producer some assurance that after the food leaves his or hercontrol, the food will be in an acceptable condition when it reaches theretail grocery store and ultimately, the consumer.

In meat packaging, in particular, packaging systems which provideextremely low levels of oxygen are desirable because it is well knownthat the fresh quality of meat can be preserved longer under anaerobicconditions than under aerobic conditions. Maintaining low levels ofoxygen minimizes the growth and multiplication of aerobic bacteria.

One way to insure a minimal level of oxygen in a meat package is tosubject the package or rigid gas barrier materials to a vacuum in orderto remove as much of the gas in the package as possible prior to sealingthe package. The package can then be sealed and the meat maintained in a“zero” atmosphere environment (commonly referred to as vacuumpackaging). Under vacuum packaging conditions, red meat turns purple.Consumers, however, prefer to see their meat bright red. As a result,vacuum packaging has not been well accepted for consumer cuts of meat.

Another means of insuring a minimal level of oxygen in a meat package isto seal the meat in a refill modified atmosphere packaging system. Thiskind of modified atmosphere packaging technology (MAP) is so successfulthat meat can be cut and packaged several weeks before purchase andstill remain fresh. Such systems typically utilize multiple layers ofpackaging. The outside layer of packaging is generally a rigid containerwith good barrier properties. The inner layer of packaging is an oxygenpermeable film. To provide a modified atmosphere environment, theair-evacuated package is typically filled with a mixture of gasesconsisting of about 30% carbon dioxide (CO₂) and 70% nitrogen (N₂).Refilling the air-evacuated package with such a mixture of gases isbelieved to suppress the growth of anaerobic bacteria. The outer layeris peeled off just prior to presenting the consumer cut for sale at thesupermarket. This allows the meat to rebloom to a bright red color. Anexcellent example of such an evacuation and refill MAP process isdescribed in U.S. Pat. No. 5,115,624 to Garwood. Vacuum packaging andrefill MAP is very expensive for three reasons. First, the rigid part ofthe package is expensive. Second, processing speeds are slow due to thevacuum and refill steps. And third, the equipment to do these proceduresis very complicated and expensive.

Another less expensive means of insuring a minimal level of oxygen in ameat package is to use a gas flush MAP process. The complicated steps ofevacuating the package and refilling with the desired gas mixture areeliminated. The outer bag (a barrier layer), is simply flushed with theproper gas mixture as it is formed around the inner container. The flushprocess reduces the oxygen content of the package to about 2%. An oxygenscavenger is placed in the package to absorb additional oxygen justprior to or simultaneously with forming and flushing the outer bag. Anexcellent example of such a MAP system is described in U.S. Pat. No.5,698,250 to DelDuca et al.

A critical feature of a gas flush MAP packaging system is the ability tokeep meat looking fresh and palatable. Oxidized meat turns anundesirable brown color. Accordingly, as discussed, an oxygen scavengeris typically placed inside the meat package in order to absorb anyresidual oxygen within the package after gas flushing and sealing thepackage. It is critically important to quickly remove the oxygen frommeat to prevent it from turning brown. Especially important inpreventing the irreversible change from red to brown is the rate atwhich oxygen is scavenged. If oxygen is removed quickly, the packagedmeat turns a purple red color. This purple red color quickly “blooms” toa bright red color upon removal of the outer layer of packaging.

Oxygen scavengers are increasingly being used in packaging systems inorder to protect various products from the detrimental effects of oxygenexposure. Several oxygen scavengers utilize the oxidation of particulateiron as a method to absorb oxygen. A small amount of water is essentialfor this reaction. In some instances, a water attracting agent such assilica gel can be used to attract water and at times to supply water inthe packet initially. A major drawback to this technology is, however,the limited amount of water that can be supplied. Typically, a majorportion of the water needed for the oxidation of particulate iron isprovided by the product and/or packaging environment being protected.This is oftentimes an inadequate amount to promote the efficient andexpedient oxidation of iron. And as mentioned, the slower the rate ofoxygen reduction, the more likely meat will turn irreversibly brown.

A need thus exists to accelerate the rate of oxygen scavengers,particularly in the confines of a modified atmosphere packaging system.It would be desirable to lower the oxygen level to about 0.04% (400 PPM)with a predetermined period of time, preferably within 90 minutes and toabout 0 within 24 hours.

SUMMARY OF THE INVENTION

The present invention provides an iron-based oxygen scavenging packetwhich exhibits an increased rate of oxygen absorption especially in theconfines of a concomitant meat packaging system. The inventionspecifically provides an oxygen scavenging packet which comprises aniron-based oxygen absorber and an oxygen uptake accelerator comprisingwater. The oxygen uptake accelerator accelerates the rate of oxygenuptake of the iron-based absorber and typically an optimum amount can bedetermined for a given iron-based absorber, above which the rate ofoxygen uptake is reduced. In a preferred embodiment, the inventionprovides an oxygen scavenging packet where an optimum ratio of between0.2 and 1.4 mL of oxygen uptake accelerator to about 2.5 grams of ironis present in the packet. Water makes an excellent accelerator but acidsand other electron acceptors may be included.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings.

FIG. 1 illustrates an oxygen scavenging packet in which the oxygenuptake accelerator is being introduced into the packet via a syringe.

FIGS. 2a and 2 b, respectively, illustrate an oxygen scavenging packetcontaining a capsule which can be ruptured at an appropriate time torelease the oxygen uptake accelerator and a packet containing a capsulebeing ruptured.

FIGS. 3a and 3 b, respectively, illustrate an oxygen scavenging packetincluding a protruding wick for absorption of the oxygen uptakeaccelerator into the packet and an oxygen scavenging packet in which thewick is being dipped into the oxygen scavenger accelerator.

FIG. 4 is an isometric view of the oxygen scavenging packet of theinstant invention inside a modified atmosphere packaging system.

FIG. 5 is a graph illustrating the rate of oxygen absorption when a dryoxygen scavenging packet is introduced into a quart sized containerwhich also includes 0.5 mL of water.

FIG. 6 is a graph illustrating the rate of oxygen absorption when anoxygen scavenging packet having 0.5 mL of water injected into the packetis introduced into a quart sized container.

FIG. 7 is a graph illustrating the rate of oxygen absorption as afunction of the amount of water injected into oxygen scavenging packets.

FIG. 8 illustrates the rate of oxygen absorption in the presence ofvarying amounts of CO₂ utilizing an oxygen scavenging packet which hasbeen injected with 0.6 mL of water.

FIG. 9 is a graph illustrating the rate of oxygen absorption as afunction of the number of oxygen scavenging packets introduced into aone quart jar.

FIG. 10 is a graph showing the percent oxygen after 1 hour as a functionof the amount of acetic acid (vinegar) injected into each of two oxygenscavenging packets.

FIG. 11 is a graph showing the percent oxygen as a function of time andas a function of the material injected into the oxygen scavengingpackets.

FIG. 12 is a graph illustrating the rate of oxygen absorption as afunction of the amount of acetic acid injected into an iron containingpacket and further as a function of whether or not the packet containsimpregnated silica gel.

FIG. 13 is a graph illustrating the rate of oxygen absorption as afunction of time and the concentration of acetic acid in water.

While the invention is susceptible to various modifications andalternative forms, certain specific embodiments thereof have been shownby way of example in the drawings and will be described in detail. Itshould be understood, however, that the intention is not to limit theinvention to the particular forms described. On the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theappended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawings, FIGS. 1 through 3 (a and b) depict anoxygen scavenging packet having a liquid oxygen uptake acceleratorpresent in some form within the packet.

Specifically, FIG. 1 depicts an oxygen scavenging packet 10 containingelemental iron 12 and in which an oxygen uptake accelerator 14 isintroduced into the packet utilizing a syringe 16. Injection can beperformed manually with a syringe and hand placement of the packetinside the package. Alternatively, the injection process can beautomated by using a commercially available metering and dispensing pumpsuch as the Luft Systematic model 45/50 and appropriate conveyingequipment to position the packets for injection and then subsequently toplace the packets into a package.

FIG. 2a depicts an oxygen scavenging packet 20 containing elemental iron22 and in which an oxygen uptake accelerator 24 is present inside acapsule 26. As FIG. 2b shows, the capsule 26 may be ruptured bymechanical force at an appropriate time in order to release the oxygenuptake accelerator 24. Optimally, the capsule should be rupturedimmediately prior to or immediately after the sealing of the package inorder to properly activate the iron-based scavenger for acceleratedoxygen uptake.

FIG. 3a depicts an iron-based oxygen scavenging packet 30 containingelemental iron (not specifically shown) and in which an oxygen uptakeaccelerator 32 can be introduced into the packet by absorption onto awick 34 which protrudes from the packet. As FIG. 3b shows, the wick 34dipped into the oxygen uptake accelerator 32. An appropriate amount ofoxygen uptake accelerator 32 is absorbed through the wick 34 into thepacket 30. Optimally, the dipping occurs immediately prior to thesealing of the package in order to properly activate the iron basedscavenger for accelerated oxygen uptake.

Further information concerning the construction of the oxygen absorberpacket preferred for use in the instant invention may be obtained fromU.S. Pat. No. 5,262,375 to McKedy. The preferred oxygen absorber packetsare manufactured by Multiform Desiccants Incorporated. However, otheriron-based oxygen absorbers will work comparably well in the instantinvention.

The instant invention particularly concerns an iron-based oxygenscavenging packet which contains an oxygen uptake accelerator consistingof water or an aqueous solution of some other substance dissolved in ormixed with water. The oxygen uptake accelerator accelerates the rate ofoxygen uptake of the oxygen absorber. This effect typically has beenfound to exhibit an optimum ratio of accelerator to iron. That is, theoxygen uptake increases as more accelerator is added, until beyond theoptimum the oxygen uptake rate decreases, as will be seen in theExamples below. It has now been found that the optimum ratio ofacceleration to iron may be found in a wider range than previouslythought to be required and determined by the activity of the oxygenabsorber. Water alone will activate and accelerate iron-based oxygenabsorbers via the presence of hydronium ions in the water. However,dilute acid solutions and other electron acceptors may be added.

Acids provide increased numbers of hydronium ions which increase theoxidation rate of iron by acting as electron acceptors. These electronacceptors facilitate the ionization of neutral iron. Once ionized, theiron readily reacts with the available oxygen and water to form ahydrated iron oxide. Other electron acceptors such as the positivelycharged ions making up salt solutions or metals such as copper alsofacilitate the ionization of neutral iron.

One preferred aqueous solution of the instant invention is an aqueoussolution which contains approximately 5% acetic acid.

The introduction of water or an aqueous solution of acid, salt orappropriate metal into the oxygen absorber packet of an iron-basedoxygen absorber serves to activate and dramatically increase the rate ofoxygen uptake of the iron inside the packet. The particulate iron in thepacket, in effect, turns to rust as oxygen is absorbed from theatmosphere surrounding the packaged meat or other packaged food product.As discussed, the water or aqueous solution enhances oxygen absorptionby the iron by acting as an electron acceptor. A proposed mechanism forrust formation is as follows.

(1) Fe(s)→Fe²⁺+2e⁻

(2) e⁻+H₃O⁺→H+H₂O

(3) 4H+O₂→2H₂O

(4) 4Fe²⁺+O₂(g)+(12+2x)H₂O→2(Fe₂O₃.xH₂O)(s)+8 H₃O⁺

In step (1) ferrous ions are produced by loss of electrons from theelemental particulate iron in the packet. However, this process cannotgo very far unless there is some way to get rid of the electrons whichaccumulate on the residual Fe. One way to do this is by step (2) inwhich H₃O⁺ ions either from the water or from acid substances in thewater, pick up the electrons to form neutral H atoms. Since Fe is knownto be a good catalyst for hydrogenation reactions in general, it isbelieved that step (3) now occurs to use up the H atoms. In themeantime, the ferrous ion reacts with O₂ gas by

step (4) to form the rust and restore H₃ O⁺ required for step (2). Thenet reaction, obtained by adding all four steps is

4Fe(s)+3O₂(g)+2xH₂O→2(Fe₂O₃.xH₂O)(s).

Acid accelerates the reaction by providing excess hydronium ions (H₃O⁺)and driving step 2. Therefore, the preferred embodiment of the presentinvention utilizes a dilute aqueous solution of acid. Such acidsolutions should, of course, be compatible with food products andinclude, for instance, acetic acid and/or citric acid.

Salt solutions also drive step (2) of the aforementioned reaction byproviding an electron acceptor, thus they are suitable for use in theaqueous solution of the instant invention. Additionally, it has beenfound that adding copper to water and/or dilute aqueous solution of acidspeeds the rate of oxygen absorption by the iron. It is believed thatthe copper induces a phenomena called electrolytic corrosion. Electronsflow from the iron to the copper, where their energy is lower. Thisremoves the excess negative charge from the iron. In addition H atoms,which now form on the negative copper surface instead of the iron,detach themselves more readily from copper than from iron, thusaccelerating step (3) of the aforementioned reaction.

As shown in FIGS. 1-3 (a and b), the aqueous solution can be introducedinto the packet utilizing an injection type process. Alternatively, thesolution can be included in the absorber packet in a separate capsule orcompartment which can be ruptured at the time of sealing the meatpackage. Also, a wick could be included in, and protrude from, thepacket such that the wick could be dipped in liquid just prior tosealing the meat package.

A preferred embodiment of the present invention involves the injectionof an oxygen uptake accelerator comprising water into the MRM absorbersmanufactured by Multiform Desiccants Incorporated. This is done justprior to the placement of the absorber into a package. This can be donemanually with a syringe and hand placement or the process can beautomated by using a commercially available metering and dispensing pumpsuch as the Luft Systematic model 45/50 and appropriate conveyingequipment to position the packets for injection and then subsequently toplace the packets into a package.

The following data, depicted in FIGS. 5-13 and in Table 1 is specific toMultiform's MRM 100 scavenger packets. All of these experiments involveusing these scavengers. The MRM 100 oxygen scavengers are specificallyformulated to work in the presence of CO₂ and refrigeration. MRM 100oxygen scavengers contain approximately 2.5 grams of iron and silica gelimpregnated with a carbon dioxide generator, NaHCO₃. A carbon dioxidegenerator is utilized to replace gas volume in the sealed meat packageas O₂ is absorbed. The iron in MRM absorbers is electrolytically reducedand annealed which means that the iron is reduced by the passage ofelectric current through a solution of the iron which is in the form ofa molten salt. As one skilled in the art will appreciate, while MRM 100scavenger packets were used in the following described experiments,similarly constituted scavenger packets would be expected to havecomparably enhanced oxygen scavenging activities with the addition ofwater and other accelerators.

FIGS. 5 and 6 illustrate that the oxygen uptake accelerator, in thiscase water, must be contained within the oxygen scavenging packet inorder to increase the rate of oxygen absorption. Specifically, FIG. 5shows the decrease in percent oxygen as a function of time when 0.5 mLof water is merely present in a quart-sized jar along with an oxygenscavenging packet. As shown in FIG. 5, at 40° F. it takes approximately30 hours for the percent oxygen to be reduced to approximately 0.5%(5,000 PPM) and more than 40 hours for the percent oxygen to be reducedto near 0% oxygen. By contrast, FIG. 6 shows the decrease in percentoxygen as a function of time when 0.5 mL of water is injected into anoxygen scavenging packet which is then placed in a quart-sized jar. At40° F., it takes approximately 15 hours for the percent oxygen to bereduced to approximately 0.5% and about 20 hours for the percent oxygento be reduced to near 0% oxygen. At 70° F., oxygen is scavenged muchmore quickly.

FIG. 7 shows that the oxygen scavenging rate is maximized when 0.6 mL ofwater is present in the oxygen scavenging packet.

FIG. 8 shows that oxygen absorption appears to be independent of theamount of carbon dioxide in the container.

FIG. 9 shows that two oxygen scavenging packets absorb oxygen at nearlytwice the rate of one packet.

As shown in FIG. 10, acetic acid, commonly known as vinegar acid, worksparticularly well in accelerating the rate of oxygen absorption of anMRM oxygen scavenger packet. Specifically, the injection of 0.5 mL ofacetic acid into each of two absorber packets reduces the amount ofoxygen in a quart jar to approximately 0.1% O₂ (1000 PPM) in one hour.As shown in FIG. 11, the percent O₂ is reduced to approximately 0.04% O₂(400 PPM) in about ninety minutes when 0.5 mL of acetic acid is injectedinto each of two MRM 100 scavenger packets. Two conclusions can be drawnfrom the data in FIGS. 10 and 11. First, injected acetic acid seems towork better than plain water in increasing the rate of oxygen absorptionof an absorber packet. Second, from FIG. 10, 0.5 mL acetic acid appearsto work particularly well in increasing the rate and total amount ofoxygen absorption. In the experiments resulting in the data in FIGS. 10and 11, the starting level of oxygen in the jars was 2%, simulating theamount of oxygen which would be present after the gas flush step of agas flush MAP process. Also, the experiments were performed underrefrigeration.

Below is a table which shows the results of an experiment designed todetermine the range of amounts of water needed to be introduced into anoxygen scavenging packet containing approximately 2.5 grams of iron inorder to satisfactorily activate the packets in a gas flush MAPpackaging process for red meat.

TABLE 1 Sample Water Initial Final Color Rating - 1.5 hrs. ColorRating - 24 hrs. No. Injection Oxygen Oxygen Of Bloom (Day 8) Of Bloom(Day 9) 1 0.8 mL 1.9%  0% Dark Red Some Browning 2 0.6 mL 1.24%  0% DarkRed Bright Red 3 1 mL 2.3%  0.26% Major Browning Major Browning 4 0.4 mL2.2%  0% Dark Red Bright Red 5 0.2 mL 1.7%  0% Dark Red Dark Red 6 0.4mL 1.5% 14.9% Excluded (Leaked) Excluded 7 0.8 mL 1.7%  0% Dark Red DarkRed 8 0.6 mL 1.55%  0% Dark Red Bright Red 9 1 mL 2.2%  0% Dark Red SomeBrowning 10  0.2 mL 2.4%  0% Major Browning Major Browning

The results show that water injections greater than 0.2 mL but less than0.8 mL per 2.5 grams of iron (approximately 100 cc of absorber capacity)are required to browning of meat. For adequate oxygen scavenging, waterinjections are within this range, preferably at 0.6 milliliters. Waterinjections outside of this range resulted in a high risk of metmyoglobinformation (browning) due to initial oxygen exposure. This experiment wasperformed utilizing Multiform's MRM oxygen scavengers but other similariron-based absorbers are believed to work comparably.

EXAMPLE 1 Determination of Range of Water Volume Necessary for OptimalOxygen Scavenging of an Iron-Based Oxygen Scavenging Packet

A ten pound chunk of fresh boneless beef (five days post mortem) was cutinto ten pieces and individually placed on meat trays or a soaker pad.The meat trays had one and one half inch tall side walls. The meat andtrays were then stretch wrapped with a standard PVC film on a Hobartmachine. After wrapping, a half inch diameter hole was created throughthe PVC in one corner of the tray to allow free flow of gases in and outof this “inner package.” Next, two MRM 100 scavengers were injected witha precisely measured amount of water and attached to one of the innerpackages containing the beef. The water injections were varied from 0.2to 1 mils per scavenger. The inner package, with the oxygen absorbersattached, was then immediately run through a Fuji/Foremost form fill andseal machine and packaged in a flushed outer bag made from Print Pack861D 2.5 mil barrier film. The flush gas was approximately 80% nitrogenand 20% carbon dioxide. The initial O₂ level in the barrier bag wasmeasured through a rubber septum with a Dansensor oxygen analyzer andrecorded. The completed packages were then placed in a refrigerator andstored at 34° F. for eight days. On the eight day the final oxygen levelwas measured and the barrier bag and oxygen absorbers removed. The meatwas allowed to rebloom in the inner package for one and a half hours inthe refrigerator. At that time the packages were removed from therefrigerator and the meat visually rated for color acceptability. Thepackages were then returned to the refrigerator for another 24 hoursafter which the meat was again rated for color acceptability.

The tray that was used for the experiment detailed in Example 1 and thedata detailed in Table 1 left a significant amount of air spacesurrounding the meat, necessitating the use of two MRM 100 scavengers.However, beef has been successfully packaged on shallow wall meat traysusing only one MRM 100 scavenger with a 0.5 mL injection of acetic acid.

FIG. 12 shows that maximum oxygen absorption occurs at an amount ofvinegar between about 0.4 and 0.6 mL acetic acid. FIG. 12 alsoillustrates that maximum oxygen absorption occurs when theoxygen-scavenging packet contains silica gel impregnated with NaHCO₃ inaddition to iron. MRM-100 absorbers and other similarly formulatedabsorbers employ silica gel to absorb and release atmospheric H₂O. Asdiscussed previously, silica gel will not by itself absorb enough waterto satisfactorily accelerate the oxygen scavenging ability of the ironto allow for the preservation of meats for longer than a few days at atime. For this reason, the present inventors have affirmatively addedconcrete amounts of water to the oxygen scavenging packets of theinstant invention.

FIG. 13 shows the rate of oxygen absorption as a function of time andthe concentration of acetic acid in water. As can be seen, 5% aceticacid performs very well at accelerating the rate of oxygen absorption at30, 60 and 90 minutes. Furthermore, 5% acetic acid is very easy toobtain, being common table vinegar.

The present invention is particularly useful when used in a modifiedatmosphere packaging (MAP) process for fresh meats. The MAP process is agas flush process that initially flushes the package to an oxygenatmosphere of about 2% or less. The oxygen scavenging packet of theinstant invention is utilized to additionally reduce the oxygen level ofthe package to 400 PPM (0.04%) or less within ninety minutes.

A brief description of the typical modified atmosphere package willfollow. This description is not meant to be limiting, but instead isprovided merely to elucidate one particular use for the instantinvention.

FIG. 4 depicts a modified atmosphere package 40 including an outercontainer 42 and an inner container 44. The inner container 44 includesa conventional semi-rigid plastic tray 46 thermoformed from a sheet ofpolymeric material which is substantially permeable to oxygen. Exemplarypolymers which may be used to form the non-barrier tray 46 includepolystyrene foam, cellulose pulp, polyethylene, polypropylene, etc. In apreferred embodiment, the polymeric sheet used to form the tray 46 issubstantially composed of polystyrene foam and has a thickness rangingfrom about 100 mils to about 300 mils. The use of a common polystyrenefoam tray 46 is desirable because it has a high consumer acceptance. Theinner container 44 further includes a stretch film wrapping or cover 48substantially composed of a polymeric material, such as polyvinylchloride (PVC), which is substantially permeable to oxygen. In apreferred embodiment, the stretch film used to form the cover 48contains additives which allow the film to cling to itself and has athickness ranging from about 0.5 mil to about 1.5 mils. One preferredstretch film is Resonate™ meat film commercially available from BordenPackaging and Industrial Products of North Andover, Mass.

A food item such as a retail cut of raw meat 50 is located inside theinner container 44. Prior to fully wrapping the tray 46 with the cover48, the partially formed inner container 44 may be flushed with anappropriate mixture of gases, typically a mixture of about 30% carbondioxide and about 70% nitrogen, to lower the oxygen level in the innercontainer 44 to about 1.5 to 5%. The foregoing mixture of gasesdisplaces the oxygen within the inner container 44 during the flushingoperation. After flushing the inner container 44, the tray 46 ismanually or automatically wrapped with the cover 48. The cover 48 iswrapped over the retail cut of raw meat 50 and about the bottom of thetray 46. The free ends of the cover 48 are overlapped along theunderside of the bottom wall of the tray 46, and, due to the clingcharacteristic inherent in the cover 48, these overlapping free endscling to one another to hold the cover 48 in place. If desired, theoverwrapped tray 46, i.e., the inner container 44, may be run over a hotplate to thermally fuse the free ends of the cover 48 to one another andthereby prevent these free ends from potentially unraveling.

The outer container 42 is preferably a flexible polymeric bag composedof a single or multilayer plastics material which is substantiallyimpermeable to oxygen. The outer container 42 may, for example, includean oriented polypropylene (OPP) core coated with an oxygen barriercoating such as polyvinylidene chloride and further laminated with alayer of sealant material such as polyethylene to facilitate heatsealing. In a preferred embodiment, the outer container 42 is composedof a multilayer barrier film commercially available as product no.325C44-0EX861D from PrintPack, Inc. of Atlanta, Ga. The co-extruded filmhas a thickness ranging from about 2 mils to about 6 mils. Prior tosealing the peripheral edges of the outer container 42, the innercontainer 44 is placed within the outer container 42. Also, the outercontainer 42 is flushed with an appropriate mixture of gases, typicallyabout 30% carbon dioxide and about 70% nitrogen, to lower the oxygenlevel in the outer container 42 to about 0.05 to 5% or 500 to 50,000parts per million (PPM). Prior to or simultaneously with flushing theouter container 42, but still prior to sealing the outer container 42,the oxygen scavenging packet 52 is placed in the outer container 42external to the sealed inner container 44. The outer container 42 isthen sealed.

After a time period of about ninety minutes, the oxygen scavengingpacket 52 lowers the oxygen level in the bag from its initial level ofoxygen to less than about 0.04% or 400 PPM and most preferably to about0%. The oxygen uptake accelerator contained within the oxygen scavengingpacket 52 is responsible for this fast rate of oxygen absorption. Theoxygen scavenger 52 also absorbs any oxygen which might permeate intothe outer container 42 from the ambient environment. In FIGS. 1 through4, the oxygen scavenger 10, 20, 30, and 52 respectively, is illustratedas a packet or label which is inserted into the outer container 42 priorto sealing the outer container 42. Alternatively, an oxygen scavengingmaterial may be added to the polymer or polymers used to form the outercontainer 42 so that the oxygen scavenging material is integrated intothe outer container 42 itself.

The retail cut of raw meat 50 within the package 40 takes on apurple-red color when the oxygen is removed from the interior of thepackage 40. The meat-filled modified atmosphere package 40 may now bestored in a refrigeration unit for several weeks prior to being offeredfor sale at a grocery store. A short time (e.g., less than one hour)prior to being displayed at the grocery store, the inner container 44 isremoved from the outer container 42 to allow oxygen from the ambientenvironment to permeate the non-barrier tray 46 and non-barrier cover48. The purple-red color of the raw meat 50 quickly changes or “blooms”to a generally acceptable bright red color when the raw meat 50 isoxygenated by exposure to air.

EXAMPLE 2

A sealed 8 gram packet (TRM, Multisorb Technologies Inc.) containingabout 68 wt % iron in a porous packet made of compressed polyethylenefibers was placed in a 4 liter multilayer bag (nylon-PE-EVA, thickness 3mils (0.075 mm), tensile strength 15,000 lb/in² (103.4 MPa), oxygenpermeability 3.9 cc/100 in²/24 hours (60.4 mL/m²/24 hours)). Themultilayer bag was filled with a gas mixture of about 70 vol % nitrogen,28 vol % carbon dioxide, and 2 vol % oxygen. (Thus, the bag containedabout 80 mL of oxygen). Then a predetermined volume of deionized waterwas injected into the oxygen absorbing packet and the multilayer bag wasmaintained at 37° F. (2.8° C.). Samples were taken periodically and thegas analyzed by Dansensor Checkmate for its oxygen content. The resultsare reported in Table 2.

TABLE 2 Oxygen Content (vol %) Time (mL/H₂O) (min) 1.00 1.25 1.5 1.75 22.25 2.5 2.75 3  0 2.06 1.979 2.02 2.08 1.841 2.26 1.974 1.879 1.8831.905 1.926  45 1.257 1.011 1.066 1.008 — 0.98 — — — — —  60 — — — —0.729 — 0.712 0.696 0.747 0.84 1.084 125 0.84 0.531 0.588 0.352 — 0.331— — — — — 150 — — — — 0.0389 — 0.0609 0.0818 0.1599 0.271 0.701 350 — —— — 0 — — — — — — 355 0.016 0 0 0 — 0 0 0 0 0 0.0788

Since each packet contained about 5.44 grams of iron, the amount ofwater use in each packet may be given as follows.

mL H₂O mL H₂O/2.5 g Fe 1 0.46 1.25 0.57 1.5 0.69 1.75 0.8  2 0.92 2.251.03 2.5 1.15 2.75 1.26 3 1.38

It can be seen that for these packets, the capacity for oxygen wasgreater than those previously tested and the iron required was reducedsignificantly. The amount of water used for each 2.5 grams of iron wassimilar, however, to that found with other packets, although it exceededthe maximum as previously defined. An optimum range is confirmed inthat, if one compares the results, it is clear that the optimum rangefalls between 1 and 3 mL of H₂O, or 0.46 and 1.38 mL/2.5 grams of iron.It may be concluded that the optimum for this system is near or slightlyabove the previous maximum, which may be attributed to the increasedactivity of the iron-based absorber composition.

While the present invention has been described with reference to one ormore particular embodiments, those skilled in the art will recognizethat many changes may be made thereto without departing from the spiritand scope of the present invention. Each of these embodiments andobvious variations thereof is contemplated as falling within the spiritand scope of the claimed invention, which is set forth in the followingclaims.

What is claimed is:
 1. A method of reducing the oxygen concentration inan enclosed space comprising: a. placing an oxygen scavenging packetwithin said enclosed space, said oxygen scavenging packet comprising: i.an oxygen permeable material formed into a closed packet; and ii. anoxygen absorber within said closed packet, said oxygen absorbercomprising iron; and b. introducing a liquid oxygen uptake acceleratorcomprising water directly onto said oxygen absorber, wherein said liquidoxygen uptake accelerator is introduced in an amount relative to theamount of said oxygen absorber, such that when the oxygen uptakeaccelerator and oxygen absorber are brought into contact, the oxygenabsorber is capable of reducing the oxygen content of a predeterminedvolume containing about 2 vol % oxygen to less than 0.5 vol % oxygen ata temperature of about 34° F. in no more than 90 minutes after saidoxygen uptake accelerator and oxygen absorber are brought into contact,said oxygen uptake accelerator being present in said packet in an amountbetween about 0.2 and 1.4 mL per 2.5 grams of iron.
 2. A method of claim1, wherein said accelerator is deionized water.
 3. A method of claim 1,wherein said oxygen absorber further comprises silica gel and a carbondioxide generator.
 4. A method of claim 1, wherein said iron iselectrolytically annealed and reduced.
 5. An oxygen scavenging packet,comprising: a. an oxygen permeable material formed into a closed packetfor holding an oxygen absorber; b. an oxygen absorber comprising ironwithin the packet of (a); and c. a liquid oxygen uptake accelerator,said accelerator comprising water, said accelerator being present in anamount relative to the amount of said oxygen absorber, such that whenthe liquid accelerator and oxygen absorber are brought into contact, theoxygen absorber is capable of reducing the oxygen content of apredetermined volume containing about 2 vol % oxygen to less than 0.5vol % oxygen at a temperature of about 34° F. in no more than 90 minutesafter said accelerator and oxygen absorber are brought into contact;said oxygen uptake accelerator being present in said packet in an amountbetween about 0.2 and 1.4 mL per 2.5 grams of iron.
 6. An oxygenscavenging packet of claim 5, wherein said accelerator is deionizedwater.
 7. An oxygen scavenging packet of claim 5, wherein said oxygenabsorber of (b) further comprises silica gel and a carbon dioxidegenerator.
 8. An oxygen scavenging packet of claim 5, wherein said ironis electrolytically annealed and reduced.
 9. An oxygen scavenging packetof claim 5, wherein said oxygen uptake accelerator is contained withinan enclosed space within said packet.
 10. An oxygen scavenging packet ofclaim 5, wherein said oxygen uptake accelerator is contained within abibulous wick, said wick extending from the exterior of said packet intothe interior of said packet.